It is common knowledge that many foodstuffs are sold as emulsions and/or suspensions prepared by dispersing a suitable stock in an aqueous medium and at least pasteurizing (usually sterilizing) the final suspensions.
It is to be understood that an “aqueous medium” means herein moisture inherently present in the stock, potable water, weak suspensions of food and flavor additives in water, moisture inherent in the stock, and the water added as required by the specifications for moisture content of the final product.
Also, it is to be understood that oilseeds, which contain high concentrations of vegetable proteins and highly volatile oils of unsaturated fatty acids when dry, cannot be processed to obtain aqueous dispersions using conventional techniques such as grinding to produce flour and mixing the flour with an aqueous medium until a desired body of “milk” or paste is obtained.
As a consequence, many processes for preparing protein-oil suspensions from soybeans and/or nuts (RU 2030883 and UA 40263A) comprise soaking the stock in preferably warm potable water until swollen, removing at least a part of protective coats that have become loose, comminuting the resulting coarse suspension to produce a finely dispersed end product with a desired proportion of solids, and sterilizing the end product by heating to a temperature not exceeding 100° C.
Food and flavor additives, such as sodium chloride, mono- and/or disaccharides, vitamins, microelements and the like are added either into the water for soaking or to the suspension of seeds in an aqueous medium in the process of dispersing the seeds.
The dispersing of stock followed by heat treatment of the semi-finished product prior to packaging is suitable for the production of fluid substances such as soybean milk or its modifications.
And yet pasteurization and especially sterilization of such products by an outside heat source has been a problem in that the walls of heat exchangers quickly get covered with a compact residue that is hard to remove and hence it is not practical to subject viscous, especially pasty, products to heat treatment in conventional heat exchangers.
Consequently, preferred are such processes and apparatus that are capable of inhibiting pathogenic microflora while stock is being processed for preparing high-viscosity products from oilseeds. In this way, the more efficient is the equipment and higher product sterility requirements, the lower are the costs of the process equipment, floor area and maintenance.
The first step along these lines is believed to have been made in the process that can be carried out in the apparatus disclosed in WO 98/42987 and illustrated in the attached drawings, particularly drawing FIGS. 8 and 9. The apparatus comprises a continuous-action pump and vertically disposed, generally rectangular in cross section, flow-through vessel, which is connected to a source of the fluid to be processed and to at least one user of the processed fluid through a delivery line and a discharge line respectively. The bottom portion of the vessel is connected through a circulation line to the suction side of the pump and its upper portion through a hydrodynamic cavitation stimulator to the delivery side of the pump.
The hydrodynamic cavitation stimulator is a pipe of a relatively large cross section with two symmetrical bypass pipes of a smaller cross section adapted to take off some fluid from the pump and to return it in thin disturbing streams running contrary to the main flow.
It is now common knowledge that controlled turbulence and cavitation in a circulating fluid flow are attended with a heat evolution, so the above-described apparatus is suitable for dispersing plant seeds and simultaneously heat treating the resulting dispersions.
Nevertheless, where the hydrodynamic cavitation stimulator is connected to the upper portion of the flow-through vessel having an invariable cross section adjacent its symmetry plane from top to bottom, the dispersing action practically ceases within the vessel to necessarily result in a dead zone adjacent to the bottom and in a sediment of coarse particles.
Prolongation of the dispersing action in turbulent flow (due to collisions of particles in a vortexlike motion) and a substantial decrease in sediments at the bottom (due to partially stirring it up) have been to some extent gained by way of whirling the flow of the aqueous medium. This has been achieved in a flow-through device having an axially symmetric process chamber.
The prior art processes for dispersing plant seeds, bearing closely on the invention, are disclosed in UA Patent 42365 A (specifically drawing FIGS. 13 and 14, and the corresponding portions of the description).
The prior art process for dispersing plant seeds in an aqueous medium is intended for continuous operation in a circulation circuit made up of an axially symmetric flow-through device (referred to in the patent as a means for continuously fractionating the turbulent flow of a fluid), a continuous-action pump and a suitable piping including at least one means for stimulating turbulent flow (capable of causing cavitation), which is built in the delivery line.
The process comprises:
(a) preparing a batch of starting suspension of seeds in an aqueous medium,
(b) starting the process, which incudes:
charging the batch by tangentially feeding the same via an open feeding line to a substantially vertically disposed flow-through device having an axially symmetric process chamber, the device being connected with its bottom portion through a suction line to the pump and with its upper portion through a delivery line to the means for stimulating turbulent flow,
dispersing (as the feeding continues) the plant seeds in the aqueous medium by pumping the suspension through the circulation circuit (the discharge outlet being closed) to cause the suspension move in turbulent flow with attended heating thereof prior to its entry into the flow-through device and whirling the flow within the device,
cutting off feeding when the circulation circuit has been filled up and the product with the seeds of a predetermined size and heated up to a predetermined temperature has been obtained,
gradually and simultaneously opening the discharge outlet and the delivery line until a continuous steady-state operation, including degassing, is achieved, wherein stock feeding and product discharge are in balance while the product temperature is practically constant;
(c) continuous steady-state operation, wherein
the circulating flow of an intermediate product with the starting suspension being admixed is continuously fed through said feeding line onto the wall of the flow-through device at its upper portion,
the product is continuously degassed and discharged for packaging through a central discharge outlet in the cover of the device, and
the intermediate product to be further circulated is continuously withdrawn from the bottom portion of the device at substantially right angles to its axis and conveyed through the circulation line to the pump;
(d) discontinuing the process by cutting off the feeding of the starting suspension and subsequently sweeping the device free of residues of the intermediate product.
The advantage of this process consists in that the intermediate product, as a result of whirling the flow, is adequately divided by centrifugal force into two fractions, one of which is rich in coarse seed particles and is circulated, while the other is sufficiently homogenized and is good for discharge.
The apparatus for carrying out the above-described process comprises:
(a) a substantially vertical flow-through device comprising a hollow housing having a flat cover and a bottom, an axially symmetric round process chamber of an invariable cross sectional area from top to bottom, and a flat dividing plate having a central opening and exposed adjacent the cover and dividing the chamber into the lower part for dispersing stock and heat treating the intermediate product, and the upper part of a substantially smaller volume and communicating with the atmosphere, for degassing the target product;
(b) a continuous-action circulating pump having the suction side connected to the device at its bottom portion, while the delivery side of the pump is connected through at least one tangential line to the upper portion of the device below the dividing plate;
(c) at least one means for stimulating turbulent flow (capable of causing cavitation) arranged between the delivery side of the pump and the inlet of the housing communicating with at least one tangential delivery line;
(d) a feeding line for feeding stock to the dispersion area, which feeding line being optionally connected to the inlet of the means for stimulating turbulent flow;
(e) an axially symmetric round flow-through thermostatically-controlled chamber for the target product, which chamber is of a smaller diameter than the process chamber, is rigidly attached to the dividing plate and has an inlet in the bottom end wall, which inlet is coaxial with the opening in the dividing plate;
(f) a pipe for discharging the end product, which pipe is connected to the degassing chamber via a substantially central opening in the cover of the flow-through device;
(g) valves built in at least the feeding line and the pipe for discharging the end product.
In practice, such apparatus have proved useful in the production of both soybean milk and viscous products from soybeans and hence from other oilseeds. In the thermostatically-controlled chamber, which is arranged in the area of greatest possible temperatures, it has been possible to heat the target product to a temperature sufficient for taking substantial moisture (together with gases that have escaped from the target product) to the atmosphere.
However, even with continuous dividing of the whirling flow into two fractions the continuous feeding of whole seeds to the peripheral zone of the device for dispersing coincident with the continuous taking of the mobile dispersion for thermostatic control followed by the discharge of the condensed product through the central opening in the cover of the device is possible on condition that the described apparatus is provided with at least one means for stimulating turbulent flow that is capable of stimulating vigorous cavitation within the circulating fluid.
It is obvious for those skilled in the art that the more vigorous is cavitation, the higher temperature of the fluid in the process chamber is attainable. In particular, the temperature can exceed 120° C., at times 130° C. Such temperatures and intensive mixing of the matter being dispersed result in thermomechanical and thermochemical destruction of oils and proteins, which alone may deteriorate organoleptic quality of the product, especially where the flow of seed particles is being slowed down and they are settling to the bottom where they undergo prolonged heating.
Also, it has been experienced that the aqueous media used in dispersing soybeans necessarily contain dissolved air, oxygen included; and an appreciable amounts of air are drawn into the circulation circuit together with stock being continuously fed.
Under vigorous cavitation, the molecules of dissolved air can break down to atoms. In such singlet state, chemical activity of oxygen drastically increases to cause uncontrolled oxidation destruction of oils and proteins and, consequently, to more noticeable quality deterioration of the pasty products produced from oilseeds.
As a consequence, the prior art process and apparatus are usually used to produce slightly condensed soybean milk for use as fodder or an ingredient of combination fodder for grazing farm animals.